Clerodendrum trichotomum Thunberg—An Ornamental Shrub with Medical Properties

Harlequin glory bower (Clerodendrum trichotomum) is a shrub or small tree belonging to the Lamiaceae family, native to Japan, Korea, and eastern China. It has esthetic value and in Europe, it is cultivated as an ornamental plant. Its sweet-smelling flowers have a white or pink crown. The calyx turns from green to pink–purple over time, providing an especially decorative touch around surrounding the ripe deep-blue fruits that persist until winter. In the areas of its natural occurrence, the leaves and young shoots of C. trichotomum, and sometimes the roots, flowers and fruits, are used in folk medicine due to its anti-inflammatory, analgesic, anticancer, sedative, and hypotensive effects. Products based on Harlequin glory are also used in the treatment of rheumatoid arthritis, joint pain, skin inflammation, or asthma. Preliminary research on the composition of raw material suggests that its health-promoting effect is associated with the presence of numerous secondary metabolites, including phenylpropanoids, flavonoids, lignans, terpenoids, steroids, alkaloids, and anthraquinones. This work reviews the current state of knowledge about the phytochemistry and in vitro and in vivo pharmacological properties of the extracts and main active components isolated from C. trichotomum. It also indicates that before it can be used in modern medicine, further research is necessary regarding the safety and efficacy of the raw material, its mechanisms of action, and dosage.


Introduction
The use of conventional drugs is often supplemented by the use of medicinal plants as therapeutic agents, with herbal remedies being more available and less expensive.According to the World Health Organization (WHO), herbal medicines meet the healthcare needs of approximately 80% of the world's population, especially in developing countries [1].Although medicinal plants have been used in treatments for millennia, scientific research on their beneficial effects has gained popularity only in the last few decades.Such research is particularly poor concerning species outside of traditional European medicine.
One particularly diverse taxon that has been utilized in traditional and folk medicine for centuries in India, China, Japan, Thailand, and some areas of Africa is the genus Clerodendrum.Dozens of species from this genus have been used as anti-inflammatory, antidiabetic, antihypertensive, antimalarial, antiviral, hypolipidemic, antioxidant, and anticancer agents [2][3][4][5][6][7].However, despite the seemingly promising potential, only a few of these species have been studied so far with regard to their chemical composition and pharmacological properties.
The genus Clerodendrum L. initially belonging to the Verbenaceae family, according to the APG system (Angiosperm Phylogeny Group), has been assigned to the Lamiaceae [8,9].It was first described by Linnaeus in 1753, based on the species Clerodendrum infortunatum found in India.Although the name was changed to Clerodendron (from the Greek words: klero-chance and dendron-tree) ten years later, the Latin name was reintroduced in 1942 by Moldenke and is currently the most commonly used [10].
Clerodendrum is a genus comprising about 580 species, including small trees, shrubs, and herbaceous plants.They are primarily found in the tropical and subtropical zones of Asia, Australia, America, and Africa [2,10].Several species can be found in the temperate climate zone, but they are primarily cultivated as ornamental plants.One of the species, sometimes found in gardens around Europe due to its relative frost resistance, is the species from Japan and China: C. trichotomum.
The aim of this paper is to present the current state of knowledge about C. trichotomum, with particular emphasis on its botanical characteristics, chemical composition, and traditional use, as well as the biological activity of its raw materials and bioactive compounds.This review also aims to generate interest in this intriguing and beautiful species, which remains relatively unknown in Europe.Promising results from studies on its composition and activity encourage further efforts to deepen our understanding of this species.This is particularly important because modern requirements for medicinal raw materials necessitate the use of only detailed, tested, and standardized products, whereas there are no established official therapeutic indications, administration forms, dosages, or safety profiles for C. trichotomum and its bioactive compounds.

Methodology of Paper Selection
The papers were selected from the following electronic databases: Google Scholar, scientific databases (PubMed, Scopus, and Web of Science), and various publishers as well as Flora of China using different relevant keywords.The following search phrases were used: "Clerodendrum trichotomum", "morphology of Clerodendrum trichotomum", "Clerodendrum extracts", "phytochemisty of Clerodendrum", "properties of Clerodendrum", "biological activities of Clerodendrum", "phytoconstituents of Clerodendrum", "taxonomy of Clerodendrum", toxicology of Clerodendrum", ethnopharmacology of Clerodendrum", and "medicinal uses of Clerodendrum".Searches were conducted without imposing any language restrictions, but papers published in languages other than English without an available English abstract were rejected.
Ultimately, 39 published reviews and experimental studies from the period 1970-2022 were selected, of which 11 concerned the isolation of bioactive compounds from C. trichotomum, 11 biological activity of C. trichotomum extracts and its secondary metabolites, 13 were a combination of phytochemistry and biological activity of the species, one was related to the morphology of the species, and three were reviews of several plants from the Clerodendrum genus, including this species.Most biological studies were based on simple in vitro tests.Studies conducted on animals were few and only fragmentary, and none were clinical studies.
Among the activity studies, only papers describing products (infusions, extracts, and the fractions obtained from them) and compounds isolated directly from C. trichotomum were included.Studies involving synthetic compounds were excluded, as well as studies reporting the compounds isolated from other plant species known to be present in C. trichotomum.This applies especially to acteoside, a compound with such numerous, widely-documented biological activities that it is even the subject of separate reviews [11][12][13].

Distribution and Morphology of C. trichotomum
Clerodendrum trichotomum (Harlequin glory bower, Chance tree, Japanischer Losbaum, Chou-Wu-Tong) occurs naturally in lowland and mountainous areas in Japan, Korea, and eastern China [2], where it grows as a shrub or small tree, reaching heights of 1.5-10 m.In Europe, it rarely reaches a tree-like form, and when planted as an ornamental plant in gardens, it usually does not exceed 2 m in height.
The stems and leaves of C. trichotomum have soft hairs and emit an unpleasant odor when crushed.The leaves are opposite, dark green, up to 20 cm long, and variable in shape: ovate-elliptic, triangular-ovate, or ovate, with a broadly cuneate, truncate, or, rarely, heart-shaped base and a sharply pointed apex.The length of the leaf petioles ranges from 2 to 8 cm [14].The plant blooms from August to October.Inclined dichotomous inflorescences, 8-20 cm long, appear at the ends of branches.Each individual flower has a diameter of about 2-3 cm, emits a sweet fragrance, and its corolla is white or pinkish.The calyx is greenish but gradually turns pink-purple.It is deeply lobed with five distinct lobes, triangular, lanceolate, or ovate in shape, pointed at the ends.The fruits are round and about 6-8 mm in diameter.Ripe ones are deep blue in color [14].Surrounded by a pink, persistent, enlarged calyx, they look particularly decorative and persist until winter.However, in colder climate zones, the plants may not produce any fruits at all.
A plant cultivated in greenhouse conditions and transplanted three months earlier at the beginning of the third growing season into the garden in Central Europa is given in Figure 1.

Applications in Traditional Folk Medicine
In China, and other regions where the plant grows wild, preparations from the leaves, stems, flowers, roots and fruits of C. trichotomum have been used for centuries in folk medicine [15].Reports indicate that the leaves and stems demonstrate significant antiinflammatory activity [3,4] and are applied in the treatment of inflammatory skin conditions.In Chinese medicine, the raw material is also recommended for eczema.It has anti-itching and mildly analgesic properties [4,15].C. trichotomum has been recommended for the treatment of malaria and dysentery [8].The leaves of the plants have anti-rheumatic effects [4,16].Decoctions are used in the treatment of rheumatoid arthritis, joint pain, numbness, and paralysis.Moreover, the species was used as an anti-asthmatic agent [2].In folk medicine, C. trichotomum is used for hypertension due to its calming and hypotensive properties [4,6].It is also believed to have anti-diabetic properties [2].Additionally, there are reports that the fruits may have anticancer potential [17].

Overview of Bioactive Compounds Identified in C. trichotomum
The first studies focusing on the chemical composition of C. trichotomum were carried out in the 1970s [18].Since then, various phenolic compounds, including phenylpropanoids, flavonoids and lignans, terpenoids, steroids, alkaloids, anthraquinones, and essential oils have been detected in the plant [19] (Figure 2).

Phenolic Compounds
Phenolic compounds are widely represented in the genus Clerodendrum [2].Their presence directly correlates with the biological activity of raw materials.Phenolic compounds may occur as free molecules or bound to sugar residues.The dominant group of phenolic compounds in C. trichotomum are phenylpropanoids.

Alkaloids
The first compound isolated from C. trichotomum was the blue trichotomine (112), present in the fruits of this species, along with its sugar derivative, trichotomine G1 (113) (Figure 36).Earlier attempts to isolate this pigment took place in the 1940s but were unsuccessful [38].Several years later, indolizino [8,7-b] indole 5-carboxylic acids were obtained, which are precursors to trichotomines [39].Petroleum ether extract of C. trichotomum leaves was found to contain an alkaloid with a structure that was confirmed by spectroscopic analysis as 1H-indole-3-carboxylic acid (114) (Figure 37).In the study, this compound was obtained for the first time from the Clerodendrum genus [34].

Biological Activity of C. trichotomum
In the last decade, some attempts have been made to confirm the biological activity of C. trichotomum and identify the metabolites responsible for it.

Anti-Inflammatory Activity
The main application of C. trichotomum is connected to its anti-inflammatory potential.Research based on murine RAW 264.7 macrophage cell lines and mouse and rat models found that inflammation induced by carrageenan in rat paw was reduced by 23% with the application of a 60% methanol leaf extract fraction of C. trichotomum at a dose of 1 mg/kg.The same product reduced capillary permeability induced by intraperitoneal injection of acetic acid in mice by 47% and inhibited prostaglandin E2 (PGE2) production in RAW 264.7 macrophages treated with lipopolysaccharide (LPS).All these effects were at least as strong as those obtained in the tests for indomethacin, indicating significant anti-inflammatory activity [3].
A subsequent report found that the methanol fraction of the leaf extract of C. trichotomum significantly reduced the amount of PGE2 in a dose-dependent manner, with isoacteoside (1) and acteoside (7) identified as the main compounds exhibiting this activity.Further experiments included tests on vascular permeability in mice and a carrageenan-induced edema model in rats.The 80% methanol fraction reduced dye leakage with a maximum inhibitory activity of 47.0%, with similar inhibition reported for pure acteoside (46.5%).In the carrageenan-induced edema model, the 80% methanol fraction reduced the frequency of edema occurrence by 59.5%, and acteoside by 63.8% [22].
Research on the anti-inflammatory effects of C. trichotomum was also conducted by a Korean research team at Jeju National University.The ethyl acetate fraction obtained from a 70% ethanol extract of the leaves effectively inhibited nitric oxide (NO) production in LPS-stimulated RAW 264.7 cells, with an IC 50 of 18.87 µg/mL.Application of this fraction (100 µg/mL) also effectively reduced tumor necrosis factor α (TNF-α) and interleukin-6 (IL-6) levels, as well as the expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) in RAW 264 cells stimulated by LPS.These results indicate the promising anti-inflammatory potential of the product [4].
A mixture of six plant ferments, including one obtained from C. trichotomum, was administered to mice with allergic rhinitis induced by egg albumin.A product, fermented for 4 days, reduced allergic symptoms with a similar effectiveness to cetirizine.It also significantly reduced the levels of histamine and immunoglobulin E in the blood, which were released during contact with the allergen.Additionally, the ferment mixture containing C. trichotomum was found to inhibit the activity of COX and 5-LO enzymes, which are generators of pro-inflammatory mediators [40].

Antioxidant Activity
Several studies describe the evaluation of the antioxidant activity of methanolic extract of C. trichotomum and its constituent compounds.The first report examined the antioxidant activity of jionoside D (4) based on its ability to scavenge intracellular free radicals and neutralize DPPH (1,1-diphenyl-2-picrylhydrazyl) radicals.At a concentration of 10 mg/mL, jionoside D reduced intracellular ROS levels by 86%; the result was comparable to the control (N-acetylcysteine).It also neutralized approximately 55% of DPPH free radicals at a concentration of 10 mg/mL.Additionally, jionoside D inhibited lipid peroxidation in hamster lung fibroblasts treated with hydrogen peroxide (H 2 O 2 ), increased cell viability, prevented H 2 O 2 -induced apoptosis, and enhanced the activity of the enzymes superoxide dismutase (SOD) and catalase (CAT), protecting against oxidative stress [5].
The antioxidant properties of trichotomoside (8) were also examined.It was found to effectively scavenge intracellular reactive oxygen species (ROS) and DPPH radicals, and it increased the viability of cells exposed to γ-radiation and H 2 O 2 , with greater efficacy observed against the former.Like jionoside D, trichotomoside scavenged intracellular radi-cals more effectively than DPPH radicals, suggesting that it acts not only as a conventional radical scavenger but also indirectly stimulates the cellular defense system [17].
The studies also showed that the crude, unfractionated methanolic extract of C. trichotomum exhibited DPPH radical scavenging activity, with an IC 50 value of 33 µg/mL and iron ion reduction at a level of 1045 mM Fe(II)/g dry weight [41].DPPH radical scavenging activity was also examined for recently-isolated polyketones and lignans.It was found that all lignans of C. trichotomum (19)(20)(21)(22) possessed moderate antioxidant activity, with IC 50 values ranging from 53.6 µM to 68.9 µM, whereas the polyketones, clerodendruketone A (110) and B (111), did not [26].

Antiviral Activity
Studies have investigated the potential of the phenylpropanoids of C. trichotomum to inhibit HIV-1 integrase (human immunodeficiency virus) [21].The strongest activity was reported for acteoside (1) and isoacteoside (7), with IC 50 values of 7.8 µM and 13.7 µM.While significant inhibition against HIV-1 integrase was also exhibited by leucosceptoside A (2), plantainoside C (3), and jionoside D (4) (29.4-60.9µM), no such activity was observed for martynoside (5) or isomartynoside (6).These results suggest that for phenylpropanoid glycosides to inhibit HIV-1 integrase, they require two catechol groups, and the activity of these compounds decreases as the number of methoxy groups in the aromatic ring increases.However, the location of the feruloyl or caffeoyl substituent in the sugar part does not significantly influence the activity [21].
Chathuranga et al. [42] investigated aqueous extracts from C. trichotomum and its main component acteoside (1) for their activity against RSV (respiratory syncytial virus).It was found that both products limited virus replication and the death of virus-infected cells, with IC 50 values of 27.95 µg/mL for the extract and 15.64 µg/mL for acteoside.The extract from C. trichotomum leaves and acteoside reduced the level of viral mRNA and virus protein synthesis.Additionally, in studies on a mouse model, the formation of syncytia was inhibited, preventing the spread of the virus [42].

Antibacterial Activity
A study of the antibacterial activity of n-hexane, methylene chloride, ethyl acetate, and n-butanol fractions of C. trichotomum extract against Staphylococcus aureus, Escherichia coli, and Helicobacter pylori found the methylene chloride fraction to be active against H. pylori; in addition, the compounds isolated from it, 22-dehydroclerosterol (106) and β-amyrin (79), had moderate activity against S. aureus and E. coli at a concentration of 3.4 mg/mL [36].In another study, ethanol extract of C. trichotomum inhibited the growth of both Grampositive and Gram-negative bacteria, such as S. aureus, E. coli, Proteus vulgaris, and Klebsiella pneumoniae [38].
Furthermore, the antibacterial activity of polyketones isolated from C. trichotomum leaves against Escherichia coli and Staphylococcus aureus was analyzed by turbidimetry.Clerodendruketone A (110) at a concentration of 50 µg/mL exhibited a bacteriostatic effect ranging between 30% and 60% against Escherichia coli, and between 60% and 80% against Staphylococcus aureus.In contrast, for clerodendruketone B (111), the values for the two tested microorganisms ranged from 30% to 60% [26].

Antihypertensive Activity
One of the traditional uses of C. trichotomum preparations is to lower blood pressure.Oral administration of C. trichotomum leaf extract reduced blood pressure in spontaneously hypertensive rats, but not in normotensive animals.Intravenous administration resulted in the dilation of renal vessels, increased urine flow, and sodium excretion leading to blood pressure reduction [6].
Subsequent studies have evaluated the inhibition of angiotensin-converting enzyme (ACE) by phenylpropanoids isolated from the stem of C. trichotomum: acteoside (1), leucosceptoside A (2), martynoside (5), isoacteoside (7), and isomartynoside (6).The following respective IC 50 values were obtained: 373 µg/mL, 423 µg/mL, 524 µg/mL, 376 µg/mL, 505 µg/mL.This indicates that the strongest effect was demonstrated by acteoside and isoacteoside.Furthermore, it appears that the antihypertensive action of C. trichotomum is at least partially due to the inhibitory effect of its phenylpropanoid glycosides on ACE, with this effect increasing with increasing numbers of hydroxyl groups on the aromatic rings [44].
Teas from the leaves and flowers of C. trichotomum were orally administered to spontaneously hypertensive rats for eight weeks to estimate their effect on blood pressure and heart rate.After this period, it was found that systolic blood pressure in the rats had decreased by 12.5%, diastolic blood pressure by 44.9%, and heart rate by 24.5%, compared to untreated controls; these differences were all significant [7].

Activity in Metabolic Diseases
The effectiveness of C. trichotomum tea in lowering cholesterol levels has been documented.Oral administration for a period of eight weeks reduced body weight, total cholesterol, and triglycerides in rats by between 20 and 30% compared to the control group [7].
Jang et al. [45] evaluated the effect of a 70% methanol extract from C. trichotomum leaves on metabolic disorders induced by a high-fructose diet.The extract was administered to rats with water for 16 weeks at a dose of 500 mg/kg body weight.It was found that the C. trichotomum extract alleviated the effects of a high-fructose diet by reducing body weight gain and hyperglycemia, and it improved the disruption of serum lipid profiles in rats.Additionally, the product alleviated insulin resistance and liver steatosis by influencing the signaling pathways of AMP-activated protein kinase, peroxisome proliferator-activated receptor α (PPARα), and sterol regulatory element-binding protein 1; hence, it may be a promising therapeutic agent against metabolic disorders [45].
The effect of the raw material on hyperuricemia and associated inflammation has also been examined.In the first experiment, C. trichotomum leaves were extracted using 70% ethanol, and the obtained extract was fractionated using hexane, chloroform (CHCl 3 ), ethyl acetate (EtOAc), and n-butanol (BuOH).The study evaluated the ability of individual fractions to inhibit xanthine oxidase activity, thus reducing uric acid production and protecting against hyperuricemia.It was shown that the strongest inhibitors were the CHCl 3 (IC 50 = 4.43 µg/mL) and EtOAc (IC 50 = 5.69 µg/mL) fractions [4].
In the second study, a leaf extract of C. trichotomum at a dose of 400 mg/kg body weight was administered to mice with hyperuricemia induced by potassium oxonate.The supplementation significantly reduced the levels of uric acid and creatinine in the blood while increasing their levels in the urine.Moreover, the extract alleviated inflammation and apoptosis induced by potassium oxonate by increasing the level of anti-apoptotic Bcl-2 and decreasing the level of pro-apoptotic Bax in kidney tissues [46].

Other Activities
It has been found that 7-O-glucoside of apigenin (10b) isolated from C. trichotomum leaves can inhibit reflux esophagitis and gastric inflammation in rats.Administration of the compound reduced the volume of gastric juice, increased gastric pH, and significantly reduced the size of lesions induced by exposure of the gastric mucosa to indomethacin [23].

Toxicity of Clerodendrum Plants
Although no toxicological data currently exists on C. trichotomum and its products, some reports exist for other species in the genus, suggesting that they may be safe for use.However, this does not eliminate the need for such testing of C. trichotomum.
The leaf and root extracts of C. infortunatum given orally for 15 days at 2 and 3 g/kg body weight did not cause changes in body weight or movement patterns in Swiss albino mice compared to controls [47].Also, biochemical, hematological, and histopathological studies revealed no significant differences to the control.The extracts of this species thus appear safe and non-toxic for animals.In addition, the ethyl acetate, chloroform, ethanolic, and aqueous extracts of C. inerme did not demonstrate any observable toxicity, and all hematological and biochemical parameters were found to be within the normal range [48].Another study assessed the acute and sub-acute toxicity of hydroethanolic leaf extract of C. polycephalum in rats for 24 h and 28 days.It showed that treatment with 1 g/kg, 2 g/kg, and 5 g/kg of extract revealed no lethality in the animals following acute toxicity testing.No significant differences were noted in any hematological parameters or in most biochemical parameters, compared to controls, suggesting that long-term administration is generally safe [49].No mortality or abnormal behavior was observed in rats receiving an aqueous extract of C. phlomidis leaves orally at doses of 200, 400 and 800 mg/kg/day for 90 days.However, mild-to-moderate changes were observed in liver and kidney biochemical markers, which correlated with histopathological findings after high doses [50].

Conclusions and Future Prospective
Medicinal plants and their phytochemicals have demonstrated a wide range of pharmacological effects and have made a significant contribution to the prevention and therapy of numerous diseases.Traditional medicine is also a valuable resource for designing new treatments.In particular, herbal remedies appear suitable for preventing and treating prevalent lifestyle diseases.
The present work provides an overview of current knowledge regarding the promising pharmacological activities associated with C. trichotomum and its various bioconstituents.Although the scientific data on its activities are not extensive, studies conducted over the past twenty years suggest it may play a role in treating many ailments.Its extracts and those of its isolated components have anti-inflammatory, antioxidant, cytotoxic, antiviral, and anti-hypertensive properties, and they are effective in treating metabolic disorders.Its biological activity appears to be associated with its phenylpropanoid, flavonoid, terpenoid, and steroid content.Furthermore, cyclohexylethanoids, anthraquinones, lignans, and alkaloids have been identified in the extracts and may also play a role in the activity of the raw material.
C. trichotomum appears to have high potential as a treatment, which encourages further research in this area and the recognition of this species beyond its aesthetic values.However, the data regarding the raw material are still too scarce to meet contemporary standards set for official medicinal products.To ensure appropriate dosing, effectiveness, and safety, any plant substance used for pharmaceutical, dietary, and cosmetic purposes requires detailed chemical analysis, confirmation of its efficacy in in vitro, in vivo, and clinical studies, and standardization using validated analytical methods.
In the face of these demands, the raw material and its products need to be included in clinical studies to confirm their therapeutic significance and justify their use.The current successful reports related to the efficacy of the bioactive ingredients of C. trichotomum and its extracts are fragmentary, and most studies have employed a relatively simple methodology.Additionally, most studies have focused on in vitro experiments whose results lack clinical applicability.In future, to clarify the specific biological mechanism, more advanced strategies should be used; preclinical and clinical trials are needed to study the targets of active compounds of C. trichotomum extracts.Also, no standardized method exists for obtaining and preparing products to ensure they exhibit sufficient dosage, high activity, durability, and safety.As such, future research should assess the bioavailability, pharmacokinetics, distribution, and metabolism of products obtained from C. trichotomum in the human body.

Figure 1 .
Figure 1.Clerodendrum trichotomum: a two-year-old plant transplanted in the spring in the current growing season from a pot to the ground.

Figure 38 .
Figure 38.Chemical structures of other compounds present in C. trichotomum.